Method for beneficiating clay by flotation



United States Patent 3,337,048 METHOD FOR BENEFICIATLNG CLAY BYFLOTATION Venancio Mercade, Metuchen, N.J., assignor to Minerals &Chemicals Philipp Corporation, Woodbridge, N.J., a corporation ofMaryland No Drawing. Filed Dec. 2, 1964, Ser. No. 415,503 20 Claims.(Cl. 209-5) This invention relates to the beneficiation of clay and isdirected especially to a process for floating finely-divided coloredimpurities from the clay.

Clay, especially kaolin clay, is widely used as a pigmentfor coatingpaper. For such use, the value of the clay is dependent upon itswhiteness or brightness since this property affects the appearance ofclay-coated sheet material. High-grade coating clays have brightnessvalues of at least about 86-87% when the brightness is determined by alight reflectance method hereinafter described. Small differences inbrightness values of clays represent significant differences in theutility of the clays. Thus, a clay that has a brightness of 91.0% ismarkedly superior to a clay having a brightness of 89.0% or even 90.0%.

Some clays, especially certain foreign primary kaolin clays, possessadequate brightness for paper coating use after being beneficiated onlyto the extent that coarse agglomerates and grit are removed. Otherclays, such as the sedimentary kaolin clays, as exemplified by Georgiakaolin clay, normally contain an appreciable quantity of finely dividedcolored impurities which detract significantly from the usefulness ofthe clays. These sedimentary clays, after degritting and fractionationto remove oversize, have a brightness which is far below the brightnessvalues of high grade coating clays.

The colored impurities that ness of sedimentary kaolin clays includeferruginous matter. This constituent can be removed at least in partfrom the clay by chemical bleaching methods, such as with hydrosulfurouscompounds, which solubilize the ferruginous matter so that it can beremoved from the clay. Sedimentary kaolin clays usually also containanatase, which is a yellow titaniferous impurity that has a verydetrimental effect on the clay brightness. This type substantiallyunaffected by the chemical by the clay industry. To remove coloredtitaniferous impurities, it has been necessary to employ froth flotationin the presence of flotation reagents which bring about the selectiveflotation of the titaniferous matter from the clay. The flotationbeneficiated clay is then treated with chemical bleaching reagents tosolubilize and eliminate a substantial amount of the undesirableferuginous matter. The flotation of the titaniferous matter from theclay can be achieved by dispersing the clay in water, incorporating ahigher fatty acid, such as tall oil acids, aerating the system andwithdrawing a froth which is a concentrate of the yellow titaniferousimpurities originally associated with the clay. Especially good resultshave been obtained using ultraflotation, which is a particular type offlotation process. In this type of flotation process, described in US.2,990,95 8 to Ernest W. Greene et al., a substantial amount of finelydivided insoluble particulate matter, usually finely divided calcite, isincorporated into the aqueous clay dispersion along with the fatty acidcollector reagent. The added particulate matter, which is alsoreagentized by the fatty collector reagent, enhances the flotation ofthe finely divided colored impurities and reports in the froth alongwith the colored impurities. Ultraflotation in conjunction with chemicalaccount for the low brightbleaching has resulted in the commercialavailability of 90% to 91% brightness Georgia kaolin clay from claycrudes having brightness values less than These results have beenachieved with a type of discolored kaolin clay referred to in the fieldas white clay to distinguish it from gray clay which is similar to whiteclay in chemical composition but which, for reasons presently unknown,has a distinctly gray tinge.

To brighten white clay by flotation and chemical bleaching to optimumbrightness values, it has been found that it is essential to achievecomplete dispersion of the clay by means of sodium silicate beforesubjecting the clay to flotation. It has been necessary, however, tocarefully control the quantity of sodium silicate used. Even a smallexcess of the sodium silicate has been found to affect adversely theresults of the flotation operation. In many cases, adequate control ofdispersant dosage has been difficult because of individual differencesin the dispersant demand of different crudes, even crudes from differentlocalities within the same mine.

In the case of gray clay crudes, it has been necessary to resort topreliminary chemical treatment of the clay in order to achieve thedesired response of the gray kaolin clay crudes to the flotationprocess. As an example of such preliminary chemical treatment is thesulfidization treatment described in US. 3,072,255 to Ernest W. Greeneet al. Even with the specialized chemical treatment of the gray clay,the overall results were not quite comparable to the best resultsachieved with the white variety of kaolin clay.

An object of this invention is to improve the effectiveness of frothflotation as a method for removing colored impurities from clay.

One specific object is to buffer the effect of sodium silicatedispersant in clay flotation so that the clay is not so sensitive to thequantity of alkali silicate dispersant and small amounts of excessdispersant will not adversely affect flotation results.

Another object beneficiated clays.

Still another important object is to provide a process for brighteninggray kaolin clays to brightness values comparable to those of high gradewhite coating clays.

I have discovered a simple, yet remarkably elfective method forimproving upon the response of clays, includ ing gray kaolin clay, tofroth flotation.

Stated briefly, the present invention resides in dispersis to improvethe brightness of flotation whereby a dilute stable hydrosol is formedby reaction between the metallic salt and the dilute sodium silicate.The clay pulp is dispersed with the hydrosol reagent before the pulp issubjected to froth flotation in the presence of flotation reagentsselective to colored impurities in the clay. An essential feature of theprocess is that the quantity of salt that is incorporated into thesolution of the sodium silicate is restricted to quantity which forms astable hydrosol with quantity of polyvalent metal salt carying out myinvention is a small to the quantity of sodium silicate less than about2 pounds per ton of clay.

In accordance with a preferred embodiment of my invention, theaforementioned hydrosol dispersant reagent is used in combination withan alkaline carbonate cooperthat is employed in amount as compared thatis used and is the sodium silicate. Thus, the i ive dispersant and thelatter material is incorporated to a pulp of the clay before addition ofthe hydrosol spersant reagent.

The metal salts used in preparing the hydrosol reagent Intain metalcations of Group II or higher in the Periodic able. The Periodic Tablereferred to is the one appearing Kirk-Othrners Encyclopedia of ChemicalTechnology,

)1. 5, page 672. As is well known in the art, metal ions Group II orhigher react with alkaline sodium silicate aqueous media with theformation of precipitates. In re dilute systems I employ, the reactionproducts remain )lloidally dispersed in the aqueous media, formingstable ispersions usually referred to as hydrosols. Chemicalthesehydrosols probably comprise complex silicates. .xamples of metal ions ofGroup II or higher are Zinc, ianganese, cadmium, lead, nickel, silver,magnesium, alcium and aluminum. Especially preferred are salts of ietalshaving amphoteric properties, e. g., salts of alulium or manganese.Manganous salts or manganic salts an be used although the former arepreferred because f their lower cost. With white Georgia kaolin clays, Irefer to use aluminum salts. On the other hand, man- ;anese salts appearto give somewhat better results than tluminum salts with gray kaolinclay.

The following table contains data illustrating the effect f addition ofvarious quantities of aluminum sulfate to l dilute aqueous solution ofbrand sodium silicate a commercial solution reported to contain 9.16% NaO, 19.5% SiO and about 62% H O, weight basis). The lata representresults obtained by slowly adding a 1% [weight basis) aqueous solutionof alum cate to 100 parts by Weight water) and allowing the compositionsto stand for the periods of time indicated.

- precipitate is formed an anhydrous sodium silicate basis, usually 1.0to 3.0 pounds anhydrous sodium silicate per ton with most clays. Usingthe 0 brand sodium silicate (which contains about 68% water) about 2.0to 10.0, and preferably 3.0 to 6.0 pounds, of the commercial sodiumsilicate solution is used for every ton of clay. Metal salt is usuallyemployed in amount ranging from about 0.1 to 2.0 pounds per ton of clay,with especially good results being obtained with 0.4 to 0.8 pound perton. When too little metal salt is used, the effect of its presence maynot be appreciable. With too much metal salt, a copious flocculent whenthe salt is incorporated with the sodium silicate solution and the metalsalt is not so effective. Before addition of the hydrosol to the clay, Iprefer to add an alkaline carbonate cooperative dispersant to the claypulp in amount of 2.0 to 10.0 pounds carbonate per ton of clay. Withwhite clays, ammonium carbonate is the preferred carbonate. With grayclays, sodium carbonate is preferred.

In putting my invention into practice, the hydrosol dispersant reagentis formed by diluting water-soluble sodium silicate with water andslowly adding a dilute aqueous solution of polyvalent metal salt until asuitable quantity of salt solution has been added. This condition isindicated by the development of a turbid but stable system which is freefrom flocs and exhibits the Tyndall phenomenon. The hydrosol formed byreaction of the metal salt and sodium silicate is then added withagitation to an aqueous clay pulp. Sufficient hydrosol is added to forma welldispersed pulp. It is desirable to formulate the system so thatthe clay solids content of the desired pulp will be about 10% to weightbasis. The clay is agitated with the hydrosol for at least 10 minutes,preferably 30 to minutes, before incorporation of the collector reagentinto the pulp. With pulps that are to be degritted and/or fractionated,it may be convenient to carry out EFFECT OF ADDITION OF ALUM TO A DILUTESODIUM SILICATE SOLUTION Various anions can be present as the anionicconstituent of the metal salt used in preparing the hydrosol reagent andthe results that are achieved are substantially independent of theanionic constituent of the salt. Thus, the results obtained withaluminum sulfate have been found to be substantially equivalent toresults with either aluminum nitrate or aluminum chloride when thevarious salts were used in amount to provide equivalent quantities ofaluminum ions. Nitrates, chlorides, sulfates and acetates are especiallyrecommended because of their low cost and availability. However, othersalts can be employed. Mixed salts, such as ammonium alums can be used.Mixture of salts, such as, for example, a mixture of aluminum sulfateand manganese sulfate, can be employed. The use of hydrated salts isalso fully within the scope of the invention and the term metal salt asused herein is intended to encompass hydrated metal salts.

The water-soluble sodium silicates employed in the preparation of thehydrosol reagent have a weight ratio of Na O to SiO ranging from 111.60to 113.75. Excellent results have been obtained with sodium silicatehaving a Na O to SiO weight ratio of 1:322.

The sodium silicate is employed in amount ranging from about 0.5 toabout 4.0 pounds per ton of clay on such steps after addition of thehydrosol and before incorporation of collector reagents.

The marked benefit of incorporating the metal salt into the sodiumsilicate dispersant solution before incorporating the dispersantsolution into the clay is dramatically illustrated in the accompanyingexamples.

The flotation reagents used in carrying out the process of thisinvention include fatty acid reagents which are selective to the titaniaimpurities in the clay. The flotation reagents used in ultraflotationare preferred. As mentioned in US. 2,990,958 to Ernest W. Greene et al.,reagents for utraflotation concentration include, in addition to higherfatty acid, especially a mixture of resin acid and fatty acid (tall oilacids), a substantial quantity of finely divided auxiliary mineral,especially minus 325 mesh calcite and, preferably, an oil-solublewater-insoluble petroleum sulfonate salt. Additional quantities ofsodium silicate can be incorporated into the pulp after addition ofcalcite if the addition of calcite results in flocculation of the pulp.Ammonium hydroxide can be used to adjust the pH to a desired level ofabout 8.0 to 8.5. The pH can be buffered, as by the addition of ammoniumsulfate. Flotation is carried out in an alkaline pulp, producing a frothwhich is a concentrate of impurities in the clay intimately mixed withthe finely divided mineral additive. The beneficiated clay, in the formof a dispersed pulp, reports in the machine discharge product. Therecovery of beneficiated clay can be improved by refloating the frothproduct one or more times.

The following examples are given to contribute to a better understandingof the present invention and to illustrate its benefits.

Examples I to N, which follow, illustrate the application of my processto the flotation beneficiation of white sedimentary Georgia kaolin clay(Washington County clay). The minus 325 mesh fraction of this clay had abrightness of about 80% before being beneficiated by flotation andbleaching. In beneficiating the white clay, the following generaldispersion and flotation procedures were used. In some cases, theseprocedures were modified as described in the examples. In describing theprocedures, all reagents are reported on a weight basis and representpounds per ton of dry clay unless otherwise indicated.

DISPERSIONWHITE CLAY Twelve hundred and fifty grams of dry clay Wasdiluted with soft water to 30% solids, weight basis, and transferred toa Fagergren flotation cell. When used, sodium carbonate or ammoniumcarbonate was added as a 5% (weight basis) aqueous solution and inamount to provide a desired quantity of the reagent, typically 2.0 to6.0 pounds sodium or ammonium carbonate per ton of clay. The pulp Wasagitated without aeration for 1 minute. A 5% aqueous solution of brandsodium silicate was prepared by adding parts by weight 0 brand(containing about 68% H O) to 100 parts by weight water. The 5% solutionwas added to provide the desired quantity of dispersant, typically 3.0to 8.0 pounds 0" brand per ton of clay. When sodium or ammoniumcarbonate was used, the dilute sodium silicate solution was incorporatedimmediately after agitating the pulp for a minute with the carbonate.After addition of the sodium silicate solution, the pulp was agitatedfor 30 minutes in the Fagergren flotation cell and the pH recorded. Theslip was then degritted by passing it through a 325 mesh screen.

ULTRAFLOTATIONWHITE CLAY A portion of the pulp containing 750 grams ofthe degritted clay (dry clay basis) was diluted with 250 ml. soft water.112.5 grams of minus 325 mesh calcite having an average particle size ofabout 5 microns (Drikalite) was added and agitated without aeration for1 minute. The pulp in the conditioner was at about solids, weight basis.Forty-five ml. of a 5% ammonium sulfate solution was added and the pulpconditioned for V2 minute. An'emulsion of the following composition wasthen added to the pulp and conditioned for 17 minutes: 250 ml. of softwater, ml. of a 2 /2% aqueous solution of ammonium hydroxide, 137 dropsof a mixture of equal parts of crude tall oil acids and a solution ofneutral calcium petroleum sulfonate in mineral oil (Calcium Petronate).After 5 minutes conditioning time had elapsed, 111 drops of lubricatingoil (Eureka M) were added. The

Reagent: Pounds/ton Calcite 300 (NH SO 6.0 NH OH 2.0 Tall oil acidsAqueous emulsion 4.5 Calcium Petronate {4.5 Eureka M oil 8.0

the pH of the pulp at the end of conditioning was typically 8.5-8.8.

The conditioned pulp was subjected to aeration and froth flotation in a1000 cc. Air Flow flotation cell, removing a froth product for 10minutes. The froth product was refloated three times without addition ofreagents, producing three products: a froth product (F.P.); a firstmachine discharge product (MD1); and combined machine discharge product(MD-2, 3,. 4). MD-l typically contained about 6.5% solids and MD-Z, 3, 4about 2.5% solids. The machine discharge products were analyzed by astandard chemical method for TiO and, in some cases, they were alsoanalyzed chemically for Fe O Brightness values of products weredetermined by TAPPI Standard Method T-646 m-54, as described on pages159A and A of the October 1954 issue of TAPPI (a monthly publication ofthe Technical Association of the Pulp and Paper Industry). The methodmeasures the light reflectance of a clay sample and thus gives aquantitative indication of its brightness or whiteness.

BLEACHING-WHITE CLAY The machine discharge products were flocced byaddition of sulfuric acid in amount to reduce the pH to 2.5. The floccedclay was bleached with zinc hydrosulfite solution, following typicalpractice of the industry. The clay was then filtered. The brightness ofthe clay after being bleached Was measured and compared to thebrightness of the clay after flotation but before bleaching for thepurpose of determining the further improvement in brightness resultingfrom the chemical bleach.

Example I To illustrate the desirable effects of incorporating a smallquantity of polyvalent metal cations into a sodium silicate dispersantsolution, a series of ultraflotation tests was made with samples of the80% brightness white Georgia kaolin clay crude using sodium. silicatedispersant solution with and without addition of alum to form ahydrosol. In these tests the sodium silicate dosage was varied over arelatively wide poundage (3 to 8 pounds 0 brand sodium silicate per tonof clay). Also, tests were made with the pH of the clay dispersionincreased by incorporation of sodium carbonate or ammonium carbonate tothe clay slip before addition of the sodium silicate solution orhydrosol formed by addition of a metal salt to a 5% 0 brand sodiumsilicate solution. The results are summarized in Tables I, II and III.

TABLE I.EFFECT OF ADDING ALUM TO SODIUM SILICATE DISPERSANT SOLUTIONSlip Treatment, lbs/ton Properties of MD-l 0" Brand 1 Unbl. Br., T102,wt. FeaOs, wt. Na CO; (NH4) 1003 Sodium Alum pH 1 percent percentpercent 7 Silicate 1 Wet basis (including water present in thecommercial solution). 3 pH of dispersed Slip before addition offlotation reagents.

8 Unbleached brightness.

TABLE II.EFFECT OF PRESENCE OF ALUM ON QUANTITY OF SODIUM SILICATEEMPLOYED IN DISPERSING CLAY 1 Wet basis.

TABLE IIL-EFFECT OF VARIATION OF QUAN- TITY OF ALUM AT CONSTANT QUANTITYOF SODIUM SILICATE Slip Treatment, lbs/ton Unbleached Brightness AF 9Brand oi MD-l, (NH4) 10 0; Sodium Alum Percent Silicate 1 Wet basis.

2 Difierence between unbleached brightness of beneficiated product andhead.

Data in Table I show that while the results were generally better whenthe pH of the clay dispersion was in- :reased by addition of sodiumcarbonate or ammonium :arbonate, in all instances the addition of alumto the sodium silicate dispersant solution to form a hydrosol resultedin brighter clay products having lower TiO contents than when the sodiumsilicate was employed without alum addition. Thus, using a mixture ofalum with sodium silicate to form a hydrosol, the flotation beneficiatedclay had an excellent unbleached brightness of 87.8% and contained only0.18% TiO versus an unbleached brightness of only 84.9% with arelatively high T102 content of 0.26%.

Data in Table II show that the use of alum with sodium silicate obviatedthe normal tendency of the sodium silicate to decrease the brightness ofthe clay product very significantly when the silicate poundage was inthewhite clay dispersion and flotation procedures described above werecarried out with addition of alum at various points of the process. Inall cases, 25 ml. of a 5% ammonium carbonate solution was added to 1250grams of the Washington County crude previously blunged in water to 30%solids and the dispersant composition was then added to thecarbonate-treated slip and conditioned for 1 minute.

In one experimental test, representing a preferred sequence ofprocessing, the alum was incorporated by mixing 100 ml. of 5% 0 brandsodium silicate solution (5 parts by weight 0 brand to 100 parts byweight water) with 25 ml. of 1% alum solution for 30 minutes, adding theresulting stable hydrosol to the clay pulp and agitating withoutaeration for 30 minutes. Another test, also representing a preferredprocessing sequence, was carried out in the same way but theconditioning time was minutes. In still another test, the sodiumsilicate and alum were added separately. In that case after addition ofammonium carbonate solution to the 30% solids clay pulp and one minuteconditioning, 100 ml. of the 5% solution of 0 brand sodium silicate wasadded and the pulp conditioned for one minute. Twenty-five ml. of 1%aqueous alum solution was then added and conditioned for 29 minutes. Inother tests, alum was added either after the calcite carrier and beforeaddition of emulsified fatty acid reagent or after the emulsified fattyacid reagent. In all cases the pulp was degritted over a 325 mesh screenafter the dispersant treatment and before being reagentized forultrafiotation concentration with calcite carrier and emulsified fattyacid reagent. The pH of the pulps were about 8.1 after dispersion anddegritting. After addition of the emulsified flotation reagents, the pHof the pulps were 8.5i0.l.

Analyses were made on MDl and on composites of MD-l and MD-Z, 3, 4(indicated as MD-l-4), with the results summarized in Table IV. The datain this table show that the titania flotation was markedly moreeflicient when the alum was mixed with the sodium silicate to form ahydrosol before the clay was dispersed with the sodium silicate thanwhen the same quantity of alum was added after the clay had beendispersed with the sodium silicate. In all cases, flotation of titaniawas improved somewhat by incorporation of the alum. The data thereforedemonstrate the beneficial eflect of alum on the flotation of titaniafrom a sodium silicate dispersed clay pulp and the desirability ofincorporating the alum with the sodium silicate to form a hydrosolbefore the sodium silicate is employed to disperse the clay.

TABLE IV.EFFECT ON FLOTATION OF METHOD OF ALUM ADDITION TO CLAY PULPSlip Treatment, lbs/ton MD-l MD-1-4 0 B and Method of Alum Addition P tP t P t P t ercen ercen ercen ercen (NHi) 2003 fl ll A12(SO4)a.18HzO Wt.T103 Wt. TiOa Silicate 1 2.0 8.0 0. 4 Alum and sodium silicate added 47.9 0.15 91. 0 0.17 as mixture (Hydrosolfl 2.0 8.0 0. 4 Alum and sodiumsilicate added 41. 7 0.15 87. 7 0. 16 as mixture (Hydrosol). 2.0 8. 0 0.4 Sodium silicate added first 48. 5 0. 19 91. 8 0. 20

followed by alum after one minute. 2.0 8.0 0. 4 Alum added after calciteflota- 51. 4 0.20 92. 2 0. 20

tion reagent. 2.0 8.0 0. 4 Alum added after emulsified 44. 4 0.19 89. 40.20

fatty acid flotation reagent. 2.0 8.0 Control, no alum added 51. 3 0.2391.8 0.22

1 Wet basis. 2 Conditioned for 30 minutes. 3 Conditioned for 60 minutes.

creased with this particular clay crude to values in excess of about 5pounds 0 brand per ton of clay.

Data in Table III show the desirable effect on clay brightness ofincorporating alum into the dispersant solution in amounts of 0.24 to1.6 pounds per ton of clay.

Example 11 To illustrate the desirability of adding polyvalent metalExample III This example illustrates the use, also in accordance withthis invention, of a manganese salt additive to a sodium silicatedispersant in the flotation beneficiation of the Washington County clay.

The previously described white clay dispersion pro cedure was modifiedas follows: ammonium carbonate as salt as a mixture with the sodiumsilicate dispersant, a 5% aqueous solution was added to a 30% solidsaqueous pul of the clay and conditioned for twominutes. The ammoniumcarbonate was used in amount of 2 pounds (NH CO per ton of crude. Inaccordance with this invention, a stable hydrosol obtained by thoroughlymixing 50 ml. of a 1% aqueous solution of MnSO .H O with 100 ml. of a 5%aqueous solution of brand sodium silicate was added to the clay pulp atroom temperature. The pulp then contained sodium silicate in amount of8.0 pounds of 0 brand per ton of crude clay and MnSO .H O in amount of0.8 pound per ton of the crude clay. After addition of the hydrosol, theclay pulp was conditioned for 30 minutes. The pulp was immediatelydegritted through a 325 mesh screen and subjected to the ultraflotationprocedure previously described. The combined machine discharge products(MD14) were fractionated by sedimentation to produce a fine sizefraction. This fine size fraction was flocced with sulfuric acid to a pHof 1.5 and thickened by sedimentation. A sample was obtained forbrightness. The remainder was bleached with zinc hydrosulfite andanalyzed for brightness.

The fine size fraction of MD-14 had an excellent brightness of 88.9%before bleaching, representing an increase of 8.1% in brightness fromthe crude. Hydrosulfite bleaching increased the brightness to 90.9%.

Example IV This example illustrates the use of a magnesium salt informing the hydrosol dispersant reagent.

The procedure of Example III was repeated with another sample of theWashington County crude, except that in dispersing the clay a 1% aqueoussolution of MgSO -7H 0 was added with agitation to the solution of Obrand sodium silicate and the resulting hydrosol was added to theammonium carbonate treated clay pulp and conditioned for 30 minutes. Thesodium silicate was used in amount of 8.0 pounds 0 brand per ton ofcrude and MgSO4-7H O was used in amount of 0.5 pound per ton of crude.The previously described ultraflotation reagents and flotationconditions were used. The combined machine discharge products of theultraflotation test (tMD14) were flocced and bleached. The product had abrightness of 87.4%, as compared to a brightness of only 86.0% for asimilar test in which no polyvalent salt was added to the sodiumsilicate dispersant. The bleached MD-14 contained 0.19% Ti0 as comparedto the 0.22% TiO content of the bleached MD-1-4 of the similar testwithout addition of metal salt to the sodium silicate dispersantsolution.

A comparison of the results of this example with results of Examples Iand II indicates that manganese and aluminum salts were considerablymore effective than the magnesium salt when incorporated with the sodiumsilicate clay dispersant to form a hydrosol.

Example V The following example illustrates the benefits ofincorporating a polyvalent metal salt in a sodium silicate dispersant inthe flotation beneficiation of a gray kaolin clay from Georgia.

The same procedures employed in dispersing and floating the WashingtonCounty clay were used with the gray kaolin clay with the followingexceptions. Sodium carbonate was incorporated into the clay pulp as a 5%aqueous solution in amount of 8.0 pounds per ton of clay crude andconditioned for 30 minutes before addition of the solution of sodiumsilicate (or hydrosol). Addition of the sodium carbonate increased thepH of the clay pulp to about 5.8. Sodium silicate was used to dispersethe sodium carbonate treated pulp in amount of 5.0 pounds 0 bran-d perton of clay. Also, with the gray clay, the dispersed clay pulp wasfractionated before ultraflotation by means of a Tollhurst centrifugeand a fine fraction recovered as an aqueous pulp. The quantity offlotation reagents used with the pulp of the Reagent: Pounds/ton Calcite(minus 325 mesh) 600 (NH4)2SO4 NH OH I- 3.0 Tall oil acids 6.2 CalciumPetronate Aqueous emulslon 6.2 Eureka M oil 8.0

Conditioning time was 30 cedure was the same used with the white clay.

A further variation was that after the flotation beneficiated gray claywas flocced with sulfuric acid, it was oxidized by treatment with asolution of potassium per manganate before being bleached with zinchydrosulfite. The permanganate treatment was carried out by adding a 1%aqueous solution of potassium permanganate to the machine dischargeproduct in amount of 5 pounds KMnO per ton of clay and agitating for 60minutes. In some tests, the permanganate treatment and zinc hydrosulfitetreatments were carried out at about F. The use of a permanganatetreatment before reducing bleach in the brightening of clay is disclosedand claimed in a copending US. patent application, Ser. No. 330,634,filed Dec. 16, 1963, by James B. Duke, which is a continuation-in-partof Ser. No. 236,685, filed Nov. 9, 1962, now abandoned.

A series of tests was run with various quantities and types of metalsalts incorporated into a 5% aqueous solution of O brand sodium silicatebefore the dispersant solution was added to a pulp of the gray clay andthe pulp subjected to froth flotation and bleaching. A control was runwithout addition of metal salt to the sodium silicate dispersantsolution.

When no metal salt was added in the control experiment, the brightnessof the flotation beneficiated, bleached gray kaolin clay was 90.6%, ascompared to a brightness of only 79.8% for a similar size fraction ofthe crude. In one test, a 1% alum solution was mixed into the 5% sodiumsilicate solution to form a hydrosol and the hydrosol was conditionedwith the gray clay pulp for 20 minutes. This addition corresponded tothe use of 5.0 pounds per ton of 0 brand sodium silicate and 0.4 poundper ton of Al (SO -18H O. The Ti0 content of the bleached beneficiatedclay in this test was 0.28%, which was appreciably less than the 0.32%TiO content of the bleached beneficiated clay in the control experiment.Using the hydrosol formed by adding alum to the sodium silicatedispersant solution, product brightness was 91.2%, a value comparable tothat of the best imported kaolin clays and the best beneficiateddomestic white kaolin clays. In another test, a 1% solution of MnSO -H Owas incorporated into the dilute sodium silicate solution and theresulting hydrosol employed in amount to provide 0.4 pound MnSO -H O perton of clay and 5.0 pounds of 0 brand sodium silicate per ton of clay.Clay brightness after bleaching and flotation was 91.5% when thishydrosol was used to disperse the clay before flotation; These resultsshow, therefore, that the gray clay could be beneficiated to a greaterextent when a pulp of the clay was dispersed with a hydrosol beforeflotation and bleaching.

I claim:

1. In a process for brightening discolored clay which comprises pulpingthe clay with water, dispersing the pulp by addition of sodium silicatethereto, and subjecting the dispersed pulp to froth flotation in thepresence of an anionic flotation reagent in an alkaline flotationcircuit, the improvement which comprises incorporating a water-solublepolyvalent metal salt into a dilute aqueous solution of the sodiumsilicate clay dispersant before minutes and the flotation prohe sodiumsilicate is incorporated into the clay pulp, the mount of polyvalentsalt being suflicient to form a stable iydrosol with said dilute sodiumsilicate.

2. The process of claim 1 wherein said polyvalent salt s a salt of ametal having amphoteric properties.

3. The process of claim .2 wherein said polyvalent salt 5 an aluminumsalt.

4. The process of claim 2 wherein said polyvalent salt s a manganesesalt.

5. The process of claim 1 wherein the said polyvalent salt is amagnesium salt.

6. The process of claim bonate is incorporated into dispersed byaddition of the solution of sodium having incorporated therein saidmetal salt.

7. The process of claim 1 wherein said clay is sedimentary kaolin clay.

8. The process of claim 1 wherein said clay is sedimentary gray kaolinclay.

9. The process of claim 1 in which said sodium silicate is used inamount ranging from about 0.5 to about 4.0

1 wherein an alkaline carsaid pulp before said pulp is silicate poundsanhydrous sodium silicate per ton of said clay and said metal salt isused in amount ranging from about 0.1 to about 2.0 pounds per ton ofsaid clay.

10. In a process for the froth flotation of kaolin clay containingfinely-divided titaniferous mineral as a colored impurity wherein a pulpof the clay is dispersed with sodium silicate and the dispersed pulp issubjected to froth flotation in an alkaline circuit with added minus 325mesh calcite and a higher fatty acid selective to both said titaniferousmineral and said auxiliary mineral, producing a froth which is aconcentrate of said titaniferous mineral intimately associated with saidauxiliary mineral and a machine discharge product which is a clay ofreduced titania content, the improvement which consists in incorporatinginto a dilute aqueous solution of the sodium silicate dispersant beforea pulp of the clay is dispersed with said sodium silicate, a smallamount, less than 2 pounds per ton of said clay, of a water-solublepolyvalent metal salt said amount being sufiicient to form a stablehydrosol with said sodium silicate.

11. In a process for the froth flotation of sedimentary kaolin claycontaining colored impurities wherein a dispersed aqueous pulp of theclay is subjected to froth flotation in an alkaline circuit in thepresence of added minus 325 mesh calcite and tall oil, the improvementwhich consists in preparing the dispersed aqueous pulp of clay by addinga material selected from the group consisting of ammonium carbonate andsodium carbonate to an aqueous pulp of the discolored clay, anddispersing the resulting pulp by adding an aqueous dispersion mediumobtained by mixing an aqueous solution of a mineral acid salt of apolyvalent metal having amphoteric properties with a dilute aqueoussolution of sodium silicate, said salt being employed in small amount ascompared to the amount of said sodium silicate and being sufiicient toform a stable hydrosol therewith.

12. The process of claim 11 in which said metal salt is an aluminumsalt.

13. The process of claim 12 in which said metal salt is aluminumsulfate.

14. The process of claim 11 in which said salt is a manganous salt.

15. The process of claim 14 in which said salt is manganese sulfate.

16. A process for separating colored titaniferous matter from Georgiakaolin clay which comprises:

forming an aqueous pulp of said clay,

incorporating an alkaline carbonate into said pulp in amount within therange of from about 2 to about 10 pounds per ton of said clay,

dispersing said pulp by adding a stable hydrosol formed by mixing adilute aqueous solution of sodium silicate having a Na O to SiO weightratio within the range of from 1:1.60 to'l:3.75 with a small amount of awater-soluble salt of a polyvalent metal having amphoteric properties,said hydrosol being used in amount to provide from about 0.5 to about4.0 pounds of anhydrous sodium silicate and from about 0.1 to about 2.0pounds of said salt per ton of said clay,

and subjecting the dispersed pulp to froth flotation in the presence offlotation reagents selective to the flotation of titaniferous matter inthe clay, producing a froth which is a concentrate of titaniferousmatter originally associated with the clay, and a machine dischargeproduct which is a concentrate of clay of reduced titania content.

17. The process of claim 16 in which said salt is an aluminum salt.

18. The process of claim 17 in which said salt is a manganous salt.

19. A process for which comprises:

forming an aqueous pulp of said clay,

incorporating sodium carbonate into said pulp,

dispersing said pulp by adding a dilute aqueous solution of sodiumsilicate to which has been added a small amount of a water-soluble saltof an amphoteric metal, the amount of said salt being suflicient to forma stable hydrosol with said sodium silicate solution,

subjecting said dispersed pulp to froth flotation in the presence ofreagents selective to colored impurities in said clay, producing a frothwhich is a concentrate of colored impurities originally in the clay anda machine discharge product which is a concentrate of clay of increasedpurity,

and chemically bleaching the machine discharge product.

20. The process of claim 19 wherein said salt is a manganese salt thatis used in amount ranging from 0.4 to 0.8 pound per ton of said clay andsaid sodium silicate is used in amount ranging from 0.5 to about 4.0pounds brightening gray Georgia kaolin clay of anhydrous sodium silicateper ton of said clay.

References Cited UNITED STATES PATENTS 2,408,656 10/1946 Kirk 252-3132,569,680 10/1951 Leek 209-5 X 2,657,183 10/1953 Bechtold 252--3132,794,783 6/1957 Podschus 252-313 2,894,628 7/1959 Duke 209-1662,990,958 7/1961 Greene 209-466 3,072,255 1/1963 Greene 209166 HARRY B.THORNTON, Primary Examiner.

FRANK W. LUTTER, Examiner.

R. HALPER, Assistant Examiner.

1. IN A PROCESS FOR BRIGHTENING DISCOLORED CLAY WHICH COMPRISES PULPINGTHE CLAY WITH WATER, DISPERSING THE PULP BY ADDITION OF SODIUM SILICATETHERETON, AND SUBJECTING THE DISPERSED PULP TO FROTH FLOTATION IN THEPRESENCE OF AN ANIONIC FLOTATION REAGENT IN AN ALKALINE FLOTATIONCIRCUIT, THE IMPROVEMENT WHICH COMPRISES INCORPORATING A WATER-SOLUBLEPOLYVALENT METAL SALT INTO A DILUTE AQUEOUS SOLUTION OF THE SODIUMSILICATE CLAY DISPERSANT BEFORE THE SODIUM SILICATE IS INCORPORATED INTOTHE CLAY PULP, THE AMOUNT OF POLYVALENT SALT BEING SUFFICIENT TO FORM ASTABLE HYDROSOL WITH SAID DILUTE SODIUM SILICATE.